Sweden observed a minute of silence on April 10 for the victims of a truck attack authorities believe was carried out by a man from Uzbekistan.

A huge crowd gathered outside the Ahlens department store at the corner of the Drottninggatan pedestrian street where an attacker driving a stolen truck plowed through shoppers and slammed into the store's facade, killing four people and injuring 15.

The crowd observed a minute of silence at noon (1000 GMT) under grey and rainy skies as flowers and candles covered the ground.

Many thanked and hugged police officers guarding the scene, some even offering them flowers, for their widely praised response to the attack.

An official ceremony was simultaneously held outside Stockholm's City Hall, attended by Prime Minister Stefan Lofven, King Carl XVI Gustaf and most of the royal family, and Stockholm mayor Karin Wanngard.

"We will never give in to violence. We will never let terror prevail," Wanngard said. "Stockholm will remain an open and tolerant city."

There has been no immediate claim of responsibility for the April 7 attack, which bore similiarities to attacks claimed by the extremist group Islamic State in which assailants drove vehicles into crowds in Nice, Berlin, and London.

The suspect, who was arrested several hours after the attack, was to be formally remanded in custody by midday on April 11 at the latest.